There are a number of instances where the provision of oxygen-enriched air, sometimes referred to as oxygen, is required to be provided at a low pressure. One particular situation where such low pressure oxygen-enriched air is required is in the health care field, both in the health care field within various institutions as well as within a patient's home. In such situations, it may be necessary to provide a continuous flow of low pressure oxygen-enriched air to a patient on an on-going basis. While such patients may be able to withstand the absence of the flow of oxygen-enriched air for short periods of time, such patients frequently are unable to withstand the absence of such a flow of oxygen-enriched air for longer periods of time without suffering major health problems. In particular, such patients are normally not able to move from one location to another without oxygen-enriched air.
Systems for the provision of a flow of low pressure oxygen-enriched air include distillation processes, adsorption separation processes and membrane separation processes. One such process is a so-called pressure swing adsorption (PSA) process which has the advantage of being able to provide oxygen-enriched air in a short period of time after the supply of a suitable feed gas e.g. compressed air, to the apparatus. An example of a pressure swing adsorption process is described in U.S. Pat. No. 4,948,391 of Y. Noguchi, which issued Aug. 14, 1990.
A typical pressure swing adsorption process applied to the provision of oxygen-enriched air could comprise the following steps:
a) introducing air under pressure into a cylinder having an adsorption column of an adsorbent which selectively adsorbs nitrogen,
b) continuing the introduction of the air into the cylinder such that a zone of the adsorbed gas (nitrogen) moves forward through the cylinder,
c) collecting the desired gas (oxygen) that passes from the cylinder,
d) terminating the introduction of air to the cylinder,
e) terminating the collection of oxygen from the cylinder,
f) discharging a portion of the pressurized gas remaining in the cylinder, and
g) returning a portion of the oxygen back into the cylinder to flow through the column in the opposite direction to desorb the gas (nitrogen) adsorbed on the adsorbent and to purge the desorbed gas (nitrogen) from the cylinder.
Steps (a)-(e) effect the separation of nitrogen from the air so as to provide oxygen-enriched air, whereas steps (f) and (g) effect regeneration of the column used in the process. This permits continuous and long-term use of the pressure swing adsorption process to provide oxygen-enriched air.
One of the disadvantages of known processes for the supply of oxygen-enriched air at low pressure is that such processes lack the flexibility to allow the patient to be located at a fixed location but also to be able to move from that location with relative ease with an assurance that the source of oxygen-enriched air is sufficient. For instance, the patient may wish or need to be able to move from a bed or other similar location, e.g. to use toilet facilities, prepare meals, go to another room or change locations for other reasons. Such mobility with existing processes generally requires a patient to be disconnected from a first source of low pressure oxygen-enriched air and to be reconnected to a second system for provision of such air and which is mobile e.g. a cylinder of oxygen-enriched air. The patient would want an assurance that the source of oxygen-enriched air is sufficient, which would be of particular concern if the patient wished to be mobile for an extended period of time e.g. a day or weekend, without having to re-fill the mobile, or ambulatory, cylinder at a dealer or distributor.